Polymerizable anaerobic compositions are precatalyzed polymerizable compositions which cure by a polymerization process which is inhibited by oxygen. As a result they remain in an unpolymerized state as long as adequate contact is maintained with air or other oxygen-bearing materials. Cure may be instituted by removing the composition from contact with oxygen. Since such oxygen free conditions can be found between closely fitting, non-porous surfaces, such as between interfitting metal parts, anaerobic compositions have found great utility in the adhesives and sealants fields.
The earliest anaerobic material is that disclosed in U.S. Pat. No. 2,628,178 to Burnett and Nordlander, issued Feb. 10, 1953. A more technically advanced and the first commercially important type of anaerobic composition is that disclosed in U.S. Pat. No. 2,895,950 to Krieble, issued July 21, 1959. Typical examples of disclosures relating to improved anaerobic compositions of this latter type may be found in the following U.S. Pat. Nos.: 3,043,820 to Krieble, issued July 10, 1962; 3,046,262 to Krieble, issued July 24, 1962; 3,218,305 to Krieble, issued Nov. 16, 1965; and 3,425,988 to Gorman and Toback, issued Feb. 4, 1969.
Improvements in the chemistry of anaerobic systems permitted the incorporation of polymerization accelerators which, while not destroying the stability of the composition over significant periods of time, such as six months or more, did provide increased speed of cure at the time of intended use. However, as more of the accelerator was added, or if a stronger accelerator was used, the incidence of spurious polymerization of the composition prior to the time of intended use increased. It also was found that these anaerobic compositions were far more sensitive to outside influences, such as temperature, and their performance was less predictable. For reasons not completely known, the number of compositions which would cure during processing or immediately after manufacture also increased.
In an attempt to solve these problems, larger amounts of conventional polymerization inhibitors (such as hydroquinone) were added to the anaerobic compositions. This tended to reduce speed of cure and did not solve the above mentioned stability problems. More powerful polymerization inhibitors were discovered, but were not found to be the complete solution to the problem. Even with these inhibitors, the stronger types of polymerization accelerators could not be used with safety, particularly at concentrations which would produce highly desirable speeds of cure.
It is the purpose of this invention to provide anaerobic compositions which can be formulated with increases in either or both stability and speed of cure, as well as to provide a process for producing anaerobic compositions having such capabilities.